What razor and a mower have in common?

It seems that nothing.

When we remove hair with razor or removal cream, we only get rid of the visible part of the hair. The root that is left in a follicle remains thick and healthy. After the visible part of a hair is removed, the root nurtures the remaining hair under the skin, making it harder and stronger. Shaving can be compared to mowing, by just cutting the surface hair and allowing regrowth.

What do we do to make the grass thicker?

We mow it regularly, and as a result the lawn becomes thicker with each cut and regrowth. Just like our hair from shaving.